Deadly Black Death bug hasn’t changed, but we have

Scientists have cracked the genetic code of the Black Death, one of history’s worst plagues, and found that its modern day bacterial descendants haven’t changed much over 600 years.

Luckily, we have.

The evolution of society and medicine — and our own bodies — has far outpaced the evolution of that deadly bacterium, scientists said.

The 14th century bug Yersinia pestis is nearly identical to the modern day version of the same germ. There are only a few dozen changes among the more than 4 million building blocks of DNA, according to a study published online Wednesday in the journal Nature.

What that shows is that the Black Death, or plague, was deadly for reasons beyond its DNA, study authors said. It had to do with the circumstances of the world back then.

In its day, the disease killed between 30 million and 50 million people — about 1 of every 3 Europeans. It came at the worst possible time — when the climate was suddenly getting colder, the world was in the midst of a long war and horrible famine, and people were moving into closer quarters where the disease could infect them and spread easily, scientists say. And it was likely the first time this particular disease had struck humans, attacking people without any innate protection.

“It was literally like the four horseman of the apocalypse that rained on Europe,” said study lead author Johannes Krause of the University of Tubingen in Germany. “People literally thought it was the end of the world.”

In devastating the population, it changed the human immune system, basically wiping out people who couldn’t deal with the disease and leaving the stronger to survive, said study co-author Hendrik Poinar of McMaster University in Ontario.

But simple antibiotics today, such as tetracycline, can beat the plague bacteria, which doesn’t seem to have properties that enable other germs to become drug resistant, Poinar said. Plus, changes in medical treatment of the sick, coupled with improved sanitation and economics, put humanity in a far better position. And there’s an immune system protection we mostly have now, Poinar said.

“I think we’re in a good state,” Poinar said. “The reason we do so well is that conditions are so different.”

People still get the disease, usually from fleas from rodents or other animals, but not that often. There are around 2,000 cases a year in the world, mostly in rural areas, with a handful of them popping up in remote parts of the United States, according to the Centers for Disease Control and Prevention. Earlier this year, two people in New Mexico were diagnosed with plague. In 1992, a Colorado veterinarian died from a more recent strain, one that scientists used heavily in their study.

To get the original Black Death DNA, scientists played dentist to dozens of skeletons.

During the epidemic in the 14th century, about 2,500 London area victims of the disease were buried in a special cemetery near the Tower of London. It was excavated in the mid-1980s with 600 individual skeletons moved to the Museum of London, said study co-author Kirsten Bos, also of McMaster University. She then removed 40 of those teeth, drilled into the pulp inside the teeth and got “this dark black powdery type material” which likely was dried blood that included DNA from the bacteria.

And when she was done, Bos returned the teeth, minus a little DNA, to the skeletons at the museum.

When the same scientists first tried mapping the bacteria’s genetic makeup, it appeared to be a distinctly different germ than what is around currently. But part of that was a reflection of working with 660-year-old DNA and newer, more refined techniques revealed less difference between the early day and modern Y. pestis bacteria than between a mother and daughter, Krause said.

That’s a surprising result, but the work was well done and makes sense, said Julian Parkhill, a disease genome expert at the Wellcome Trust Sanger Institute in Britain. Parkhill was not involved in the research but has studied the bacteria.

“Getting an effectively complete genome sequence of a bacterium that lived nearly 700 years ago is incredibly exciting,” Parkhill said.

Scientists crack Black Death’s genetic code

Scientists have mapped out the entire genetic map of the Black Death, a 14th century bubonic plague that killed 50 million Europeans in one of the most devastating epidemics in history.

The work, which involved extracting and purifying DNA from the remains of Black death victims buried in London’s “plague pits,” is the first time scientists have been able to draft a reconstructed genome of any ancient pathogen.

Their result — a full draft of the entire Black Death genome — should allow researchers to track changes in the disease’s evolution and virulence, and lead to better understanding of modern-day infectious diseases.

Building on previous research which showed that a specific variant of the Yersinia pestis (Y. pestis) bacterium was responsible for the plague that ravaged Europe between 1347 and 1351, a team of German, Canadian and American scientists went on to “capture” and sequence the entire genome of the disease.

“The genomic data show that this bacterial strain, or variant, is the ancestor of all modern plagues we have today worldwide. Every outbreak across the globe today stems from a descendant of the medieval plague,” said Hendrik Poinar, of Canada’s McMaster University, who worked with the team.

“With a better understanding of the evolution of this deadly pathogen, we are entering a new era of research into infectious disease.”

Major technical advances in DNA recovery and sequencing have dramatically expanded the scope of genetic analysis of ancient specimens, opening up new ways of trying to understand emerging and re-emerging infections.

Experts say the direct descendants of the same bubonic plague still exist today, killing around 2,000 people a year.

A virulent strain of E. coli bacteria which caused a deadly outbreak of infections in Germany and France earlier this year was also found to contain DNA sequences from plague bacteria.

For this study Poinar’s team analysed skeletal remains from Black Death victims buried in London’s East Smithfield “plague pits,” which are located under what is now the Royal Mint.

By focusing on promising specimens from the dental pulp of five bodies, which had already been pre-screened for the presence of Y. pestis, they were able to extract, purify and enrich the disease’s DNA and at the same time reduce the amount of background non-plague DNA which might interfere.

Linking the 1349 to 1350 dates of the skeletal remains to the genetic data allowed the researchers to calculate the age of the ancestor of Y. pestis that caused the mediaeval plague.

Poinar, whose work was published in the journal Nature, said the team found that in 660 years of evolution, the genetic map of the ancient organism had only barely changed. “The next step is to determine why this was so deadly,” he said.

Johannes Krause Of Germany’s University of Tubingen, who also worked on the study, said the same approach could now be used to study the genomes of all sorts of historic pathogens.

“This will provide us with direct insights into the evolution of human pathogens and historical pandemics,” he said in a statement.